Apparatus and methods for testing of acoustic devices and systems

ABSTRACT

Methods and devices are disclosed for testing an acoustic probe having transducing elements for converting between acoustic and electrical signals. An electrical signal is generated at a frequency with a testing device capable of generating electrical signals over a range of frequencies. The electrical signal is transmitted to at least some of the transducing elements to measure a complex impedance and thereby evaluate a performance of the transducing elements.

BACKGROUND OF THE INVENTION

This application relates generally to acoustic probes. Morespecifically, this application relates to apparatus and methods fortesting acoustic probes.

Acoustic imaging techniques are valuable in a wide range ofapplications. While the most notable are undoubtedly medicalapplications in the form of ultrasound imaging, acoustic techniques aremore generally used at a variety of different acoustic frequencies forimaging a variety of different phenomena. For example, acoustic imagingtechniques may be used for the identification of structural defects andfor detection of impurities, in addition to taking advantage of thenonionizing character of ultrasound radiation for imaging livingbiological bodies. Just some of the medical applications for acousticimaging include the imaging of fetuses being carried by pregnant women,the detection of tumors in various organs of the body, particularly insoft-tissue structures, and the imaging of organs when real-timeinformation is the preferred method for diagnostic functions withechocardiography.

All of these techniques rely fundamentally on the fact that differentstructures, whether they be biological or otherwise, have differentacoustic impedances. When acoustic radiation is incident on an acousticinterface, such as where the acoustic impedance changes discontinuouslybecause of the presence of a tumor in an organ, it may be scattered inways that permit characterization of the interface. Radiation reflectedby the interface is most commonly detected in such applications, butthere are certain ultrasound scanning methodologies that additionally oralternatively make use of transmitted radiation.

Transmission of the acoustic radiation towards a target and receipt ofthe scattered radiation may be performed and/or coordinated with amodern acoustic imaging system. Many modern systems are based onmultiple-element array transducers that may have linear, curved-linear,phased-array, or similar characteristics. These transducers may, forexample, form part of an acoustic probe coupled with the acoustic systemto perform the actual acoustic measurements. In some instances, theimaging systems are equipped with internal self-diagnostic capabilitiesthat allow limited verification of system operation, but do notgenerally provide effective diagnosis of the transmission and receivingtransducer elements that make up the probe itself. Degradation inperformance of these elements is often subtle and occurs as a result ofextended transducer use and/or through user abuse. Acoustic imagingsystems therefore often lack any direct quantitative method forevaluating probe performance.

There is accordingly a general need in the art for apparatus and methodsfor testing acoustic probes.

SUMMARY

Embodiments of the invention provide methods of testing an acousticprobe having a plurality of transducing elements for converting betweenacoustic and electrical signals. A first electrical signal is generatedat a first frequency with a testing device capable of generatingelectrical signals over a range of frequencies. The first electricalsignal is transmitted to selected ones of the plurality of transducingelements. A first respective complex impedance is measured with thefirst electrical signal for each of the selected ones of the pluralityof transducing elements. A performance of the each of the selected onesof the plurality of transducing elements is evaluated from the firstrespective complex impedance.

Such evaluation may include determining a capacitance from the firstrespective complex impedance, such as when the first frequency is not aresonant frequency of the each of the selected ones of the plurality oftransducing elements. Alternatively, such an evaluation may includedetermining a resistance from the first respective complex impedance,such as when the first frequency is a resonant frequency of the each ofthe selected ones of the plurality of transducing elements. The resonantfrequency may be specified by receiving an identification of theacoustic probe, and receiving a specification of the resonant frequencyin accordance with the identification of the acoustic probe to definethe first frequency. The evaluation may also alternatively comprisedetermining both a capacitance and a resistance from the firstrespective complex impedance.

In some embodiments, a second electrical signal is generated at a secondfrequency different from the first frequency with the testing device.The second electrical signal is transmitted to the selected ones of theplurality of transducing elements. A second respective complex impedanceis measured with the second electrical signal for the each of theselected ones of the plurality of transducing elements. The performanceof the each of the selected ones of the plurality of transducingelements thus comprises evaluating the performance of the each of theselected ones of the plurality of transducing elements from the firstand second respective complex impedances.

In certain of these embodiments, the first frequency is not a resonantfrequency of the each of the selected ones of the plurality oftransducing elements while the second frequency is substantially theresonant frequency of the selected ones of the plurality of transducingelements. A capacitance may be determined from the first respectivecomplex impedance and a resistance may be determined from the secondrespective complex impedance. Alternatively, a first capacitance and afirst resistance may be determined from the first respective compleximpedance and a second capacitance and a second resistance may bedetermined from the second respective complex impedance.

The first frequency may in some instance be a predetermined frequencynot dependent on an identification of the acoustic probe.

These methods may be embodied by a testing device having a body, acoupling interface, a processor, and impedance circuitry. The couplinginterface is integrated with the body and adapted for connection withthe acoustic probe. The impedance circuitry is internal to the body andcoupled with the processor. The processor is coupled with the couplinginterface and capable of generating electrical signals over a range offrequencies and has instructions to implement the methods and describedabove.

The processor may comprise a direct digital synthesizer.

The body may be sized and shaped to be portable. In addition, the bodymay have a generally arcuate shape that includes a handle adapted tointerlace with a handle on an acoustic system coupled with the acousticprobe.

Specification of the resonant frequency in those embodiments that use itmay be simplified when the testing device further comprises a storagedevice coupled with the processor so that the processor may additionallyinclude instructions to retrieve the specification of the resonantfrequency from the storage device. Also, the testing may sometimesfurther comprise a camera integrated with the body and coupled with theprocessor, which additionally includes instructions to operate thecamera to read information from a label associated with the acousticprobe.

BRIEF DESCRIPTION OF THE DRAWINGS

A further understanding of the nature and advantages of the presentinvention may be realized by reference to the remaining portions of thespecification and the drawings, wherein like reference labels are usedthrough the several drawings to refer to similar components.

FIG. 1 is a block diagram illustrating a functional structure for adevice that may be used in embodiments of the invention to test anacoustic probe;

FIGS. 2A, 2B, and 2C respectively provide structural front, and sideviews of the device illustrated functionally in FIG. 1;

FIG. 3 illustrates a structure for a probe adapter that may be used insome embodiments to interface a probe with the testing device;

FIGS. 4A and 4B illustrate series and parallel tuning arrangements of anacoustic probe;

FIG. 4C is an example of an electronic model of an acoustic transducer;

FIG. 5A provides a schematic illustration of a structure for an acoustictransducer;

FIG. 5B provides a simplified illustration of the frequency response ofan acoustic transducer for purposes of illustration; and

FIG. 6 is a flow diagram summarizing methods of testing acoustic probesin accordance with embodiments of the invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Embodiments of the invention provide methods and apparatus for testingacoustic probes that make use of measurements of complex impedance. Suchacoustic probes generally comprise a plurality of acoustic transducersto effect conversion between electrical and acoustic forms of energy.Typically, the transducers comprise piezoelectric crystals that deformin response to application of voltage. Sound may thus be generated withtransducers configured as transmitter elements through the applicationof periodically varying voltage to cause mechanical oscillation, andthereby acoustic waves, at particular frequencies. Similarly,transducers may be configured as receiver elements so that periodicdeformations that result from the impingement of acoustic waves inducethe generation of a voltage that can be detected, measured, and/or usedin applications.

While much of the discussion below specifically discusses apparatus andmethods that are suitable for testing ultrasonic probes, this isintended merely for exemplary purposes; the invention is not intended tobe limited by the operational frequency characteristics used by thetested probes. Testing of acoustic probes as described herein allows abroad range of defects to be identified, including not onlyirregularities in connection issues but also identification of acousticissues like lens delamination, array malfunctions, and other issues thatinterfere with optimal functioning of the probe. As is evident from thedescription below, this is possible because changes in the acousticcoupling of a transducer are manifested in its electrical impedance,permitting the acoustic anomalies to be determined as long as theimpedance measurement is sufficiently accurate.

FIG. 1 provides a broad functional overview of a test device 100 inaccordance with embodiments of the invention. An acoustic probe 160 maybe tested when coupled with the test device 100 through the generationof signals to provide a broadband pulse that excites all the transducerelements of the probe 160. The signals may be generated with a directdigital synthesizer (“DDS”) 104, which is a type of frequencysynthesizer capable of creating arbitrary waveforms from a referenceclock. As is known in the art, the DDS 104 may generate waveforms over arange of frequencies by using a numerically controlled oscillator thatrelies on the reference clock to provide a stable time base and therebyproduce a discrete quantized version of the desired waveform, with aperiod controlled by a digital word contained in a frequency controlregister. Embodiments of the invention typically use sinusoidalwaveforms over a frequency range of about 10 kHz-20 MHz, although otherfrequency ranges may be used in a variety of alternative embodiments,such as 100 kHz-15 MHz, 200 kHz-10 MHz, or 500 kHz-5 MHz. The desiredfrequency range of the DDS 104 corresponds to a range suitable to test avariety of different acoustic probes 160 produced by differentmanufacturers, which may have different resonant frequencies. The rangeof 10 kHz-20 MHz is appropriate to test a wide range of commerciallyavailable probes that are currently produced, but those of skill in theart will readily appreciate that other ranges may be used to accommodatetesting of a more limited or more expanded set of commercially availableacoustic probes. Alternative waveform generators may be used in otherembodiments. For example, an analog generator such as a phase-lockedloop might be used, although such analog alternatives typically havereduced frequency agility, increased phase noise, and less-precisecontrol over the output phase across frequency switching transitions.

The signal generated by the DDS 104 is routed to selected ones or asubset of transducing elements comprised by the acoustic probe 160 beingtested by a switch matrix 112 and perhaps also an adapter 116. Theability to use low voltages in measuring the impedance advantageouslyallows electronic switches to be used by the switch matrix 112 in oneembodiment, reducing the size of the unit when compared with the use ofalternative electromechical relays. In cases where a signal is routedsimultaneously to a subset group of the transducing elements, the subsetgroup may correspond to a group of neighboring transducing elements. Theswitch matrix 112 comprises a bidirectional switching array capable ofestablishing the desired connections. It is generally desirable forelectrical characteristics of the switch matrix 112 not to impact theevaluation of the transducing elements. Accordingly, an array ofminiature relays may be preferred in some embodiments oversemiconductor-based switching integrated circuitry to limit capacitiveand resistive loads. The relays may be arranged in groups to limit thenumber of traces that may be active at any given time. In addition, aregular circuit topology may be used to keep the electrical loadsubstantially constant. In one embodiment, a correction factordetermined uniquely for each element may be used to further reducemeasurement errors that may be associated with electrical loadingassociated with the switch matrix 112.

The switch matrix 112 may be considered to perform a mapping from onechannel that corresponds to the DDS 104 to a plurality of channels thatare in communication with the probe 160. In some instances, particularlyin embodiments that use solid-state switches, probes of many differentmanufacturers that make use of the some connector, such as the ITTCannon DL series, may be connected directly with the test device 100.Probes of other manufacturers that use different physicalconfigurations, such as pinless or cartridge connectors, may be coupledto the test device with an adapter 116. In some embodiments, the adapter116 is configured to provide a 1:1 mapping from transducing elements ofthe probe 160 to channels of the switch matrix 112. Thus, for example,if the probe has 192 transducing elements, the adapter 116 may map eachof 192 channels from the switch matrix 112 to one of the transducingelements. In other embodiments, the adapter 116 may instead beconfigured to provided different schemes for mapping channels from theswitch matrix 112 to transducing elements of the probe 160.

Impedance circuitry 108 coupled with the DDS 104 enables the test device100 to measure the complex impedance of the probe elements as coupledthrough the switch matrix 112 and adapter 116 at frequencies establishedby the DDS 104 in accordance with known probe characteristics. This isdescribed in further detail below.

The DDS 104 may also be coupled with other elements of the testingdevice 100, with the drawing illustrating how such individual elementsmay be implemented in a separated or more integrated manner. Inparticular, the testing device 100 is shown comprised of hardwareelements that are electrically connected with the DDS 104 via bus 118,including an input device 120, an output device 124, a storage device128, and a communications system 132. The communications system 132 maycomprise a wired, wireless, modem, and/or other type of interfacingconnection and permits data to be exchanged with external devices asdesired.

The testing device 100 may also comprise software elements, shown asbeing currently located within working memory 136, including anoperating system 140 and other code 144, such as a program designed toimplement methods of the invention. It will be apparent to those skilledin the art that substantial variations may be made in accordance withspecific requirements. For example, customized hardware might also beused and/or particular elements might be implemented in hardware,software (including portable software, such as applets), or both.Further, connection to other computing devices such as networkinput/output devices may be employed. Connections between the testingdevice 100 may thus use any suitable connection, such as a parallel-portconnection, a universal-serial-bus (“USB”) connection, and the like.

An example of a physical structure for the testing device 100 isillustrated in perspective, front, and side views respectively in FIGS.2A, 2B, and 2C. The structure in these views is merely exemplary andmany other structures may be used, but the illustrated embodimenthighlights some features that may generally be included in the physicalstructure of the testing device 100. For example, the device 100 shownin FIGS. 2A-2C is sized so as to be easily carried by hand, and includesa handle 216 to facilitate such carrying. In some embodiments, thehandle 216 may include slots (not shown) on a reverse side, allowing thedevice 100 conveniently to be hung on a wall near while the probe 160 isbeing tested. The handle 216 may also be adapted to interlace with ahandle on an acoustic system coupled with the probe 160 being tested. Asevident most clearly from the side view of FIG. 2C, the device 100 mayalso have a generally arcuate shape in which the handle 216 and bottomof the device 100 act as legs to support the device 100 when it isrested on a flat surface like a table or floor. The arcuate shape ispreferred over a flat shape because it presents a display screen 208comprised by the device 200 in a position where in may be more easilyconsulted by an operator. The display screen 208 may function as theoutput device 124 shown functionally in FIG. 1, and in embodiments inwhich the display screen 208 comprises a touch screen may additionallyfunction as the input device 120 shown functionally in FIG. 1.

The device 100 may also include a camera 206 that may also correspond tothe input device 120 in the functional drawing of FIG. 1. Such a camera206 enables capturing an image associated with the acoustic probe 160 tobe studied. Such an image may record information about the probe 160,which may be determined by a variety of different mechanisms. In oneembodiment, for example, the camera 206 may be used to read a label fromthe acoustic probe 160 that identifies the probe 160 with suchinformation as the identity of the probe manufacturer, a model number,and the like. Such identification information may be provided directlyas part of the label or the label may provide a reference identifierthat may be cross-referenced with identification information stored inthe storage device 128 or in a remote storage accessible with thecommunications system 132. Label information may be read using any of avariety of techniques known in the art, including the use ofcharacter-recognition or barcode-reading techniques. In embodimentswhere barcode labels are used, any appropriate barcode symbology may beused, including one-dimensional and two-dimensional symbologies.Examples of one-dimensional symbologies include Codabar, Code 11, Code128, Code 32, Code 39, Code 93, EAN-13, EAN-8, EAN-99, EAN-Velocity,Industrial 2 of 5, Interleaved 2 of %, ISBN, UPC-A, UPC-E, and othersymbologies. Examples of two-dimensional symbologies include Aztec Code,Code 16K, PDF417, Compact PDF417, Micro PDF417, Macro PDF417,DataMaxtrix, QR Code, Semacode, and other formats. In addition,embodiments of the invention may accommodate both monochromatic andcolor barcode symbologies, including, for example, the High CapacityColor Barcode (“HCCB”) symbology.

In addition to these features, the device 100 includes a couplinginterface 104 for connection to the system to be tested and may alsoinclude one or more communications ports 212 for wired interconnectionwith computational or other devices. The communications ports 212 may becoupled with the communications system 132 of FIG. 1 and may take anyappropriate configuration, including USB, Firewire, serial, parallel,PS/2, SCSI, and other types of communications ports. Alternative to thewired interconnection is wireless interconnection, which may beimplemented using any secured or unsecured wireless communicationsprotocol known in the art.

The coupling interface 204 is particularly adapted to integrate with anacoustic probe 160 and may correspond to the adapter 116 shownfunctionally in FIG. 1. Advantageously, the coupling interface 204 maybe configured for integration with a variety of different probestructures. In one embodiment, for instance, the coupling interface 204is configured for interfacing with a physical-configuration connectorsuch as the ITT Cannon DL series of connectors. An an example of such aconnector is illustrated with FIG. 3. The connector 300 includes a body304, a shaft 312, and a plurality of retractable pins. The connector 300may be coupled with a probe 160 using the shaft 312, with contact by anumber of the pins 308 varying in accordance with the size and shape ofthe probe 160. Particularly with such a connector 300, the couplinginterface 204 enables the device 100 to test probes from manymanufacturers without the need for additional individual adapters.

The relevant electrical structure for probe transducers is illustratedin FIGS. 4A-4C. The complex impedance of each of the transducing elementmay be determined through interrogation of that element by generating awaveform at one or more appropriate frequencies with the DDS 104 andmeasuring the response of the impedance circuitry 108. In someinstances, this method may be complicated by a probe structure thatprovides a significant contribution to the imaginary part of the compleximpedance in the form of an additional source of capacitance. Inparticular, each transducing element may comprise a piezoelectriccrystal used to perform the electrical-acoustic conversions. The probemay supply energy to each such piezoelectric crystal with a coaxialcable that has an intrinsically high capacitance. Probe manufacturersaccordingly often use a tuning circuit to tune out the capacitance ofthe coaxial cable and thereby permit effective energy coupling into thepiezoelectric crystal. Any suitable tuning circuit known to those ofskill in the art may be used, such as with a standard second-order tunedcircuit. The tuning circuit typically comprises an inductive element,which may be provided in series or in parallel with the piezoelectriccrystal. Methods of the invention may account for the specificconfiguration of the tuning circuit in different embodiments.

FIG. 4A, for example, shows the electrical structure of aseries-inductor tuned probe 404 in which energy is coupled into thepiezoelectric crystal 410 comprised by each transducing element with acoaxial cable 408. The circuit for tuning out the capacitance of thecoaxial cable 408 comprises an inductive element 412 provided in serieswith the piezoelectric crystal 410, and may also include a resistiveelement (not shown), usually provided in parallel with the piezoelectriccrystal 410. FIG. 4B similarly shows the electrical structure of aparallel-inductor tuned probe 406. In this instance, the tuning circuitcomprises an inductive element 412′ provided in parallel with thepiezoelectric crystal 410′, and may also include a resistive element(not shown), usually also provided in parallel with the piezoelectriccrystal 410′.

Testing of both series-inductor tuned probes may thus be performed in amanner similar to that used for an untuned probe. In particular, the DDS104 may provide waveforms at appropriate frequencies to enable thecomplex impedance to be determined with the impedance circuitry 108. Theseries-inductor tuned probe 404 generally permits even lower frequenciesto be used than does the parallel-inductor tuned probe 406 becausevery-low-frequency waveforms may generate a small inductive reactancewith the parallel-inductor tuned probe 406. In either instance, though afrequency may be chosen that is outside the active range of thepiezoelectric crystal 410, 410′ to avoid spurious interference withoperation of the probe. In particular, frequencies may be used that arebelow the resonance frequency of the piezoelectric crystal 410, 410′.Typically used piezoelectric crystals have resonant frequencies in therange of 2-20 MHz and while it is possible to use a differentoff-resonance frequency determined individually for each probe, this isnot necessary and impedance measurements may be made at the samefrequency for each probe. In some embodiments, the off-resonancefrequency is a predetermined frequency in the range of 0.5-1.5 MHz, suchas at 1.0 MHz.

FIG. 4C provides an electrical model of the piezoelectric transducer 410or 410′. It is noted that this is one of a number of differentelectrical models that may be used but is adequate to illustrate theelectrical behavior of the testing device 100 as it interacts withacoustic probes. The voltage across the crystal is proportional to theintensity of the acoustic signals generated or received by the crystal.The inductance L 424 corresponds to the seismic mass and inertia of thesensor itself. The capacitance C_(e) 420 is inversely proportional tothe mechanical elasticity of the sensor and the capacitance C₀ 432represents the static capacitance of the transducer, resulting from aninertial mass of infinite size. Of particular interest is the resistanceR 428, which corresponds to the leakage resistance of the transducerelement. An infinite value of R in the model indicates that there is noenergy leakage, a configuration that may be achieved with theoff-resonance frequencies discussed above.

Measurements of the complex impedance according to embodiments of theinvention captures all of the electrical information represented withthe model, enabling a variety of different types of performance issuesto be diagnosed. Determination of a capacitance from the compleximpedance permits a number of potential connection issues to beevaluated. For example, capacitance determinations may be used toidentify defects associated with the coaxial cables used to coupleenergy to the respective piezocrystals. The capacitance is aparticularly useful discriminant for this type of diagnosis because itis approximately proportional to the distance along the cable where adefect occurs. If interrogation of a particular transducing elementresults in no capacitive part of the complex impedance, the respectivecable may not be connected with that transducing element. Ifinterrogation of that transducing element instead results in acapacitive part of the complex impedance that is a fraction of what isotherwise expected for a properly functioning transducing element, therespective cable may be broken or otherwise damaged at a point along itslength that corresponds to the fractional capacitance value.

Other information that may be determined from the capacitive part of thecomplex impedance is more limited. FIG. 5A provides an example of aphysical structure of a transducer element 504. It comprises a backing508 over which the piezoelectric crystal 512 itself is provided. Anacoustic lens 516 over the piezoelectric crystal 512 provides electricalisolation of the piezoelectric crystal 512 as well as acoustic impedancematching, and may be covered with a metal layer 520 such as a layer ofgold. While issues such as delamination of the acoustic lens 516 fromthe piezoelectric crystal 512 or the presence of a crack 524 or similardamage to the piezoelectric crystal 512 may be suggested by thecapacitive component of the complex impedance, the resistive part of theimpedance provides greater diagnostic information. For example, a lackof electrical signal is suggestive of both conditions, with aconcomitant capacitance matching with fully functioning transducerelements suggesting lens delamination and a concomitant mismatchsuggesting damage to the piezoelectric crystal 512.

A second complex-impedance measurement at resonance enablesdetermination of a resistive component since the resistance R 428 in themodel of FIG. 4C then takes a finite value that can be compared with anexpected resistance characteristic of a functioning transducer. Even incircumstances where an electrical signal exists, a deviation in theresistance provides diagnostic information of a defect in the transducerthat may not be available from capacitance information alone. Forexample, for some probes the resolution is too small for a capacitancemeasurement to give adequate information for reliable diagnosis of adefect. The full information available from the complex impedancepermits verification both that the transducer element is properlyconnected and that it is behaving as expected for a functioningtransducer.

This may be better understood with reference to FIG. 5B, whichsimplifies the frequency response of a piezoelectric sensor for purposesof illustration. Between the high-pass cutoff and the resonant peak 540,there is a substantially flat region 544 that is normally usedoperationally. A measurement of the complex impedance in this flatregion 544 combined with a measurement at the resonance frequencypermits considerably enhanced diagnostic information to be extracted.The expected resistance at resonance may depend on the particularcharacteristics of the probe being tested. Accordingly, a set ofacceptable resistance ranges may be stored for each probe type thetesting device 100 is configured to test, either locally at the storagedevice 128 of the testing device 100 itself or remotely so that suchranges are accessible to the testing device 100 with the communicationssystem 132. The acceptable range may depend not only on the specificprobe type, but also on the array itself and perhaps also on theloading.

Deviation of the resistance outside the acceptable range is particularlyuseful for diagnosis of issues with the transducer itself. For example,if the piezoelectric crystal 512 is cracked as illustrated in FIG. 5A,the effective size of the element is reduced, driving the resistance R428 to a value that represents less energy coupling and also less energyloss in the piezoelectric element.

Methods of the invention are accordingly summarized with the flowdiagram of FIG. 6. While the flow diagram sets out specific steps in aspecific order, this is merely intended to be illustrative. Moregenerally, there are embodiments within the scope of the invention inwhich certain of the identified steps are omitted, embodiments in whichadditional steps not specifically identified are performed, andembodiments in which some of the steps are performed in a differentorder than appears in the drawing. For example, while the flow diagramincludes complex-impedance measurements both on- and off-resonance, suchmultiple measurements are not necessary in all embodiments and thecomplex impedance might be determined at only a single frequency.

The method begins at block 604 by receiving an identification of theacoustic probe type. This information may be received by the testingdevice in any of several ways. For example, the camera 206 might be usedto read a barcode or other type of label. Alternatively, a technicianoperating the testing device 100 might use the input device 120 in theform of a touchscreen or otherwise to enter an identification of theprobe type. The identification of the probe type at block 604 isrelevant because of the capability of the testing device 100 to test avariety of different probes. Such identification specifies a number ofparameters that are relevant to interpreting the complex-impedancevalues determined from measurements performed on the probe. Thisincludes not only the resonant frequency of the probe, which isdetermined by the testing device 100 from the identification at block608, but also the acceptable capacitance and resistance values.

At block 612, a signal is generated by the DDS 104 of the testing device100 at an off-resonant frequency. As previously noted, the frequencyused for this signal, which is transmitted to the probe elements atblock 616, may conveniently be the same for every probe type byexploiting the fact that there is a limit to the value of the resonancefrequency for most commercially available acoustic probes. But inalternative embodiments, the off-resonant frequency value may alsodepend on probe type.

At block 620, the off-resonance complex impedance is measured. Inprinciple, both the real and imaginary parts of the complex impedancecontain diagnostic information, although it is generally expected thatthe imaginary component corresponding to the capacitance is most usefulsince the resistance off-resonance diverges. Accordingly, theoff-resonance capacitance is determined from the measured compleximpedance at block 624.

At block 628, a signal is generated by the DDS 104 at the resonancefrequency for the transducers of the particular acoustic probe beingtested and is transmitted to the probe elements at block 632. Again, inprinciple, both the real and imaginary parts of the complex impedancemeasured at block 636 have diagnostic information that may be used, butthe real component that corresponds to the resistance as determined atblock 640 is of particular utility.

At block 644, the performance of the probe is evaluated using thecollected impedance information, which may include complex impedancevalues at a plurality of frequencies for each transducing elementcomprised by the acoustic probe. The ability of the testing device 100in this way to measure a true complex impedance over a range offrequencies advantageously permits it to be used for the measurement ofa variety of different acoustic probes, which may have various tuningcircuits, without needing a special adapter. Furthermore, the structureand functionality of the testing device 100 permit the measurements tobe taken without the need to provide acoustic coupling with a waterbath, gel, or similar material for acoustic-impedance matching. Elementswitching that is tolerant of high voltage pulses is also unnecessary.Without the need to include a water bath, reflection target, andhigh-voltage switching, the device may accordingly be configured asdescribed herein as a self-contained, battery-powered, portable unit.

Having described several embodiments, it will be recognized by those ofskill in the art that various modifications, alternative constructions,and equivalents may be used without departing from the spirit of theinvention. Accordingly, the above description should not be taken aslimiting the scope of the invention, which is defined in the followingclaims.

1-32. (canceled)
 33. A method of testing an acoustic probe having aplurality of transducing elements for converting between acoustic andelectrical signals, the method comprising: generating a first electricalsignal at a first frequency with a direct digital synthesizer; routingthe first electrical signal via a switch matrix to a subset of theplurality of transducing elements; measuring a first respectiveelectrical complex impedance of an electrical structure of the subset ofthe plurality of transducing elements with the testing device inresponse to the first electrical signal; and evaluating a performance ofthe subset of the plurality of transducing elements from the firstrespective complex electrical impedance of the electrical structure ofthe subset of the plurality of transducing elements.
 34. The methodrecited in claim 33, wherein evaluating the performance of the subset ofthe plurality of transducing elements comprises determining a capacitivepart associated with the first respective electrical complex impedancewith the testing device.
 35. The method recited in claim 33, whereinevaluating the performance of the subset of the plurality of transducingelements comprises determining a resistive component associated with thefirst respective electrical complex impedance with the testing device.36. The method recited in claim 33, further comprising: receiving anidentification of the acoustic probe; and retrieving a specification ofa resonant frequency in accordance with the identification of theacoustic probe to define the first frequency.
 37. The method recited inclaim 33, wherein evaluating the performance of the subset of theplurality of transducing elements comprises: determining a capacitancepart of the first respective electrical complex impedance with thetesting device; and determining a resistive component associated withthe first respective electrical complex impedance with the testingdevice.
 38. The method recited in claim 33, further comprising:generating a second electrical signal at a second frequency differentfrom the first frequency with the testing device; transmitting thesecond electrical signal to the subset of the plurality of transducingelements; and measuring a second respective electrical complex impedanceof the electrical structure of the subset ones of the plurality oftransducing elements with the testing device in response to the secondelectrical signal, wherein evaluating the performance of the selectedones of the plurality of transducing elements is based on the first andsecond respective electrical complex impedances.
 39. The method recitedin claim 38, wherein: the first frequency is not a resonant frequency ofthe subset of the plurality of transducing elements; and the secondfrequency is substantially the resonant frequency of the subset of theplurality of transducing elements.
 40. A testing device for testing anacoustic probe having a cable connected to a plurality of transducingelements for converting between acoustic and electrical signals, thetesting device comprising: a direct digital synthesizer that generates afirst electrical signal at a first frequency and transmits the firstelectrical signal; a switch matrix connected to route the firstelectrical signal from the direct digital synthesizer to a subset of theplurality of transducer elements; and an impedance circuitry connectedto allow the testing device to measure a first respective electricalcomplex impedance of the subset of the plurality of transducing elementsin response the first electrical signal, wherein the testing deviceevaluates a performance of the subset of the plurality of transducingelements using the measure of the first respective electrical compleximpedance by the impedance circuitry.
 41. The testing device recited inclaim 40, further comprising an adapter configured to couple theacoustic probe to the switch matrix of the testing device.
 42. Thetesting device recited in claim 40, further comprising a body that theimpedance circuitry is internal to, the body configured to be portable.43. The testing device recited in claim 40, wherein the testing deviceevaluates the performance of the subset of the plurality of transducingelements based on a measure of a capacitive part associated with thefirst respective electrical complex impedance.
 44. The testing devicerecited in claim 43, wherein the testing device evaluates theperformance of the subset of the transducer elements of the acousticprobe based on the measure of the capacitive part associated with thefirst respective electrical complex impedance relative to a capacitivepart expected for a properly functioning probe to determine anoccurrence of a defect with the cable of the acoustic probe connected tothe testing device.
 45. The testing device recited in claim 40, whereinthe testing device evaluates the performance of the subset of theplurality of transducing elements based on a measure of a resistivecomponent associated with the first respective electrical compleximpedance.
 46. The testing device recited in claim 45, wherein thetesting device evaluates the performance of the subset of the transducerelements of the acoustic probe based on a comparison of the measure ofthe resistive component of the first respective complex impedancerelative to an acceptable range in determining a defect in the subset ofthe transducer elements.
 47. The testing device recited in claim 40,wherein the testing device evaluates the performance of the each of theselected ones of the plurality of transducing elements by: determining acapacitive part associated with the first respective electrical compleximpedance; and determining a resistive component associated with thefirst respective electrical complex impedance.
 48. The testing devicerecited in claim 40, wherein the direct digital synthesizer: generates asecond electrical signal at a second frequency different from the firstfrequency; transmits the second electrical signal via the switch matrixto the selected ones of the plurality of transducing elements; measuresa second respective electrical complex impedance of the subset of theplurality of transducing elements using the impedance circuitry inresponse to the second electrical signal; and evaluates the performanceof the subset the plurality of transducing elements using the first andsecond respective electrical complex impedances.
 49. The testing devicerecited in claim 40, wherein the testing device evaluates theperformance of the subset of the plurality of transducing elements basedon a measure of real part and an imaginary part associated with thefirst respective electrical complex impedance.